WATER QUALITY OF ATHI RIVER AND ITS TRIBUTARIES BASED ON SELECTED PHYSICAL-CHEMICAL PARAMETERS, HEAVY METALS AND BACTERIAL LEVELS

Abstract

Pollution is one of the major challenges facing water resources management in Kenya. This study was carried out to assess and monitor water quality status of the Athi River and its tributaries based on selected basic physical-chemical parameters (electrical conductivity, pH, temperature, TDS, TSS, ammonia, sulphide, nitrate, orthophosphate, BOD and COD), heavy metals (Fe, Cu, Cd, Cr, Pb, Mn and Zn) and bacteria (total coliforms, E. coli, salmonella and shigella). This is because of the perceived high pollution in Athi River and its tributaries. One hundred and ninety-two (192) water samples were randomly collected employing grab technique. The parameters were analyzed using standard methods for the examination of water and wastewater. For example, heavy metal analysis was done by digestion of 100 mL of water sample by addition of 5 ml of concentrated nitric acid in a fume chamber. Then the digested samples were analyzed using atomic absorption spectrophotometer (AAS SHIMADZU 7000, Japan). The pH (6.4 to 9.78) was generally within the standards for natural portable water while the temperature varied between 17.1 oC and 31.8 oC. The electrical conductivity (EC) ranged from 32 µS/cm to 2005 µS/cm while total dissolved solids (TDS) recorded concentration ranging from 20 mg/L to 1243 mg/L. Total suspended solids (TSS, 4 - 840 mg/L), chemical oxygen demand (COD, 14 - 3360 mg/L and biochemical oxygen demand (BOD, 1 - 640 mg/L)) recorded wide concentration range. Other parameters measured include sulphide (<1 - 192 mg/L), nitrate (ND - 44 mg/L), orthophosphate (0.1 -18 mg/L) and ammonia (ND - 204 mg/L). Levels of analyzed heavy metals were detected in the overall range of ND – 7.6 mg/L with cadmium, copper and chromium not detected. Iron levels ranged from 0.01 – 7.6 mg/L, lead ND – 0.7 mg/L, zinc ND – 3.4 mg/L and manganese ND – 4.3 mg/L. High bacterial counts recorded in collected water samples were: Salmonella (1 – 1.01×102 ) counts, Escherichia coli (4 - 1.79×107 cfu/100 mL), Shigella (1 – 1.11×102 counts) and total coliforms (20 – 6.03×107 cfu/100 mL). Some of the physical-chemical parameters (such as, BOD and COD) values in effluent samples discharged into the rivers by the wastewater treatment plants were higher than the KEBS and WHO tolerable levels. Consequently, more effort should be put by the relevant government agencies and departments to address pollution challenges in the Athi River basin